Extend vlan_splinters control behaviour

Change vlan_splinters control in openstack.json from checkbox to
radio group with 3 values: 'disabled', 'soft', and 'hard'.
'Soft' version always provides a 'trunk' field as a [0].
'Hard' version puts all vlan numbers from this interface to a 'trunk'
field.

bug 1257604

Change-Id: I9c1bbfc95eb777937bf0a9654d6f3cbc912055b9
Merge "Extend vlan_splinters control behaviour"